Avalanche Forecast

Moderate crest level NW winds will continue to transport recent snow onto lee slopes near and especially above treeline Wednesday. You will be able to trigger Wind Slabs on steep slopes near or below ridgelines. Watch for clues like variable snow height, drifts, cornices, and stiff snow that produces cracking. These are all indicators that you could trigger a Wind Slab. You can avoid triggering these avalanches by steering around steep roll-overs, unsupported features, and obvious start zones where you suspect Wind Slabs.

Small Loose Wet avalanches are possible on steep sunny slopes near and below treeline, especially during prolonged periods of sunshine. Watch for warning signs like new roller balls, pinwheels, and natural Loose Wet avalanches that indicate increasing hazard. Even small Loose Wet avalanches may carry you into terrain with high consequences such as over cliffs or into gullies. Cooler temperatures Tuesday night and Wednesday should help surface crusts form on more northerly aspects and shaded terrain. 

It has been more than three weeks since the last reported avalanche involving older weak layers. While many of these layers have not gone away, it is now difficult to trigger a Persistent Slab avalanche. We do not have any recent information if the most recent storm awakened these older weak layers. Snowpack tests can provide useful information about buried weak layers, they are not a decision making tool. 

Strong and gusty winds were seen at ridgecrest on Tuesday; DirtyFace Mt reported gusts into the 40s and Mission Ridge into the 80s for several hours. A stark drying trend was noted east of the crest with sunshine over the Wentachee Mountains and warm temperatures in all lower elevation stations. Higher elevation sites did not show any appreciable snowfall accumulation. Areas in close proximity to the Cascade crest and above 4500-5000 ft are likely the only areas the accumulated more than a few inches of snow during Tuesday's storm.  

Up to a foot of snow fell along the east slopes of the Cascades near Washington Pass from 3/21 through 3/24, with about half that amount accumulating in the East Central zone. The new snow fell on a variety of old snow surfaces. On sunny aspects, firm melt-freeze crusts were buried. In shaded locations, near surface facets and surface hoar were observed prior to the storm cycle. 

Persistent weak layers were involved in 3 avalanche fatalities over the past month. Many of these weak grain types have rounded and are no longer an issue. The remaining weak layers are generally inactive or dormant. Drastic changes to the snowpack, such as significant amounts of new snow or a major rain on snow event could make these layers a threat once again. Currently, the persistent weak layers that you may find include:

• Surface hoar and facets were buried on 3/8. This layer is typically found 18-24” (45-60 cm) below the snow surface on shaded aspects near and below treeline.
• Weak sugar-like facets (2/13 or 2/16) are 3-5 feet (90-150cm) below the snow surface. This is the most widespread persistent weak layer. It can be found just above a firm crust buried on 2/5. 
• Other shallow and very weak areas of snowpack may be found further east of the crest or in areas with less snow.

Observations

North

On Saturday 3/23, professionals near Washington Pass reported a small skier triggered avalanche in the new snow on a steep east aspect at 6500 ft. The 3/8 buried surface hoar was reported as 1.5 feet below the snow surface.

Central

None